U.S. patent application number 15/868373 was filed with the patent office on 2019-05-16 for light source for lithography exposure process.
The applicant listed for this patent is Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Li-Jui CHEN, Po-Chung CHENG, Shang-Chieh CHIEN, Tzung-CHI FU, Chieh HSIEH, Chun-Chia HSU, Bo-Tsun LIU.
Application Number | 20190150265 15/868373 |
Document ID | / |
Family ID | 66433741 |
Filed Date | 2019-05-16 |
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United States Patent
Application |
20190150265 |
Kind Code |
A1 |
HSIEH; Chieh ; et
al. |
May 16, 2019 |
LIGHT SOURCE FOR LITHOGRAPHY EXPOSURE PROCESS
Abstract
A method for generating light is provided. The method includes
generating targets with a fuel target generator. The method further
includes measuring a period of time during which one of the targets
passes through two detection positions on a path along which the
targets move. The method also includes exciting the targets with a
laser generator so as to generate plasma that emits light. In
addition, the method includes adjusting at least one parameter of
the fuel target generator or the laser generator according to the
measured period of time, when the measured period of time is
different from a predetermined value.
Inventors: |
HSIEH; Chieh; (Taoyuan City,
TW) ; CHIEN; Shang-Chieh; (New Taipei City, TW)
; HSU; Chun-Chia; (Kaohsiung City, TW) ; LIU;
Bo-Tsun; (Taipei City, TW) ; FU; Tzung-CHI;
(Miaoli City, TW) ; CHEN; Li-Jui; (Hsinchu City,
TW) ; CHENG; Po-Chung; (Zhongpu Township,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Co., Ltd. |
Hsinchu |
|
TW |
|
|
Family ID: |
66433741 |
Appl. No.: |
15/868373 |
Filed: |
January 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62586992 |
Nov 16, 2017 |
|
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|
Current U.S.
Class: |
250/504R |
Current CPC
Class: |
H05G 2/005 20130101;
H05G 2/008 20130101; G03F 7/70033 20130101 |
International
Class: |
H05G 2/00 20060101
H05G002/00; G03F 7/20 20060101 G03F007/20 |
Claims
1. A method for generating light in a lithography exposure process,
comprising: generating targets with a fuel target generator;
measuring a period of time during which one of the targets passes
through two detection positions on a moving path; exciting the
targets with a laser generator so as to generate plasma that emits
light; and adjusting at least one parameter of the laser generator
according to the measured period of time, when the measured period
of time is different from a predetermined value.
2. The method for generating light in a lithography exposure
process as claimed in claim 1, wherein the operation of measuring
the period of time comprises: projecting a first light curtain and
a second light curtain at the two detection positions; receiving
light reflected from one of the targets when the one of the targets
passes through the two detection positions; and measuring a period
of time between a time when the light reflected from the target at
a first detection position is detected and a time when the light
reflected from the target at a second detection position is
detected.
3. The method for generating light in a lithography exposure
process as claimed in claim 1, wherein the targets generated from
the fuel target generator are separated by a droplet pitch, and a
distance between the two detection positions is smaller than the
droplet pitch.
4. The method for generating light in a lithography exposure
process as claimed in claim 1, wherein the operation of exciting
the targets with a laser generator comprises irradiating a
pre-pulse laser on the targets to expand the targets; wherein the
two detection positions are located between the fuel target
generator and a lighting position where the targets are focused by
the pre-pulse laser.
5. The method for generating light in a lithography exposure
process as claimed in claim 1, wherein the operation of exciting
the targets to generate plasma comprises: irradiating a pre-pulse
laser on the targets to expand the targets at a first lighting
position; and irradiating a main pulse laser on the expanded target
to generate the plasma at a second lighting position; wherein the
two detection positions are located between the first lighting
position and the second lighting position.
6. The method for generating light in a lithography exposure
process as claimed in claim 1, wherein further comprising adjusting
a parameter of the fuel target generator according to the measured
period of time, wherein the parameter of the fuel target generator
comprises a flow velocity of the targets generated from the fuel
target generator.
7. The method for generating light in a lithography exposure
process as claimed in claim 1, wherein the parameter of the laser
generator which is adjusted according to the measured period of
time comprises a frequency for generating a laser for illuminating
the targets.
8. A method for generating light in a lithography exposure process,
comprising: generating targets with a fuel target generator;
detecting a flow velocity of the targets at a first detection
position and a second detection position on a moving path;
adjusting the flow velocity of the targets in response to the
detected flow velocity when the detected flow velocity is different
from a predetermined value; and irradiating at least one laser on
the targets to generate plasma that emits light, wherein the
targets supplied by the fuel target generator are separated by a
droplet pitch, and a distance between the first detection position
and the second detection position is smaller than the droplet
pitch.
9. The method for generating light in a lithography exposure
process as claimed in claim 8, wherein the operation of detecting
the flow velocity of the targets comprises: projecting a first
light curtain and a second light curtain at the first detection
position and the second detection position, respectively, on the
moving path; receiving light reflected from one of the targets when
the one of the targets passes through the first detection position
and the second detection position; measuring a time difference
between a time when the light reflected from the target at the
first detection position is detected and a time when the light
reflected from the target at the second detection position is
detected; and determining the flow velocity by dividing the
distance between the first detection position and the second
detection position by the measured time difference.
10. The method for generating light in a lithography exposure
process as claimed in claim 9, further comprising: calculating a
time interval by dividing an intermediate distance by the detected
velocity, wherein the intermediate distance is between the first
detection position and a lighting position where the targets are
illuminated by the laser; and wherein the laser is actuated after
the time interval when the light reflected from the target at the
first detection position is detected.
11. (canceled)
12. The method for generating light in a lithography exposure
process as claimed in claim 8, wherein the operation of irradiating
at least one laser on the targets comprises: irradiating a
pre-pulse laser on the targets to expand the targets; and
irradiating a main pulse laser on the expanded target to generate
plasma that emits light; wherein the velocity of the targets is
detected before the targets are expanded by the pre-pulse
laser.
13. The method for generating light in a lithography exposure
process as claimed in claim 8, wherein the operation of irradiating
at least one laser on the targets comprises: irradiating a
pre-pulse laser on the targets to expand the targets; and
irradiating a main pulse laser on the expanded target to generate
plasma that emits light; wherein the velocity of the targets is
detected after the targets are expanded by the pre-pulse laser and
before the expanded targets are irradiated by the main pulse
laser.
14. A light source for producing light in a lithography system,
comprising: a fuel target generator configured to generate a
plurality of targets along a moving path, wherein the fuel target
generator includes a vessel and a nozzle; a monitoring device
configured to measure a period of time during which one of the
targets passes through two detection positions, wherein the
monitoring device includes a transducer and a detector; a laser
generator configured to generate at least one laser to allow a
conversion of the targets into plasma; and a controller configured
to adjust parameters of the fuel target generator and the laser
generator according to the measured period of time, when the
measured period of time is different from a predetermined
value.
15. The light source as claimed in claim 14, wherein a distance
between the two detection positions is smaller than a droplet pitch
between two neighboring targets.
16. The light source as claimed in claim 14, wherein the laser
generator comprises: a first laser source configured to generate a
pre-pulse laser for expanding the targets at a first lighting
position; wherein the two detection positions are located between
the fuel target generator and the first lighting position.
17. The light source as claimed in claim 14, wherein the laser
generator comprises: a first laser source configured to generate a
pre-pulse laser for expanding the targets at a first lighting
position; and a second laser source positioned farther away from
the fuel target generator than the first laser source and
configured to generate a main pulse laser for exciting the expanded
targets at a second lighting position; wherein the two detection
positions are located between the first lighting position and the
second lighting position.
18. The light source as claimed in claim 14, wherein the transducer
comprises a first light source and a second light source configured
so that the targets at the two detection positions are illuminated
by light emitted from the first light source and the second light
source; wherein the detector is configured to receive light
reflected from the targets at the two detection positions when the
targets pass through; wherein the period of time is determined by
the time difference when the light from the two detection positions
are detected.
19. The light source as claimed in claim 14, further comprising a
gas supplier configured for supplying a pumping gas into the fuel
target generator so as to generate the targets; wherein the
parameter of the fuel target generator which is adjusted according
to the period of time comprises pressure of the pumping gas in the
fuel target generator.
20. The light source as claimed in claim 14, wherein the laser
generator comprises: a first laser source configured to generate a
pre-pulse laser for expanding the targets; and a second laser
source arranged farther away from the fuel target generator than
the first laser source and configured to generate a main pulse
laser for exciting the expanded targets; wherein the controller is
also configured to control a firing time frequency of the first
laser source or the second laser source according to the measured
period of time.
21. The light source as claimed in claim 14, wherein the first
light source, the second light source and the detector are disposed
on a same side of the moving path.
Description
PRIORITY CLAIM AND CROSS-REFERENCE
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/586,992, filed on Nov. 16, 2017, the entirety of
which is incorporated by reference herein
BACKGROUND
[0002] The semiconductor integrated circuit (IC) industry has
experienced exponential growth. Technological advances in IC
materials and design have produced generations of ICs where each
generation has smaller and more complex circuits than the previous
generation. In the course of IC evolution, functional density
(i.e., the number of interconnected devices per chip area) has
generally increased while geometric size (i.e., the smallest
component (or line) that can be created using a fabrication
process) has decreased. This scaling-down process generally
provides benefits by increasing production efficiency and lowering
associated costs. Such scaling-down has also increased the
complexity of processing and manufacturing ICs.
[0003] For example, there is a growing need to perform
higher-resolution lithography processes. One lithography technique
is extreme ultraviolet lithography (EUVL). The EUVL employs
scanners using light in the extreme ultraviolet (EUV) region,
having a wavelength of about 1-100 nm. One type of EUV light source
is laser-produced plasma (LPP). LPP technology produces EUV light
by focusing a high-power laser beam onto small fuel droplet targets
to form highly ionized plasma that emits EUV radiation with a peak
of maximum emission at 13.5 nm. The EUV light is then collected by
a collector and reflected by optics towards a lithography exposure
object, e.g., a wafer.
[0004] Although existing methods and devices for generating EUV
light have been adequate for their intended purposes, they have not
been entirely satisfactory in all respects. Consequently, it would
be desirable to provide a solution for increasing power conversion
efficiency from the input energy for ionization.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Aspects of the present disclosure are best understood from
the following detailed description when read with the accompanying
figures. It should be noted that, in accordance with the standard
practice in the industry, various features are not drawn to scale.
In fact, the dimensions of the various features may be arbitrarily
increased or reduced for clarity of discussion.
[0006] FIG. 1 shows a schematic view of a lithography system with a
light source, in accordance with some embodiments.
[0007] FIG. 2 is a diagrammatic view of the light source in the
lithography system of FIG. 1, in accordance with some
embodiments.
[0008] FIG. 3 is a diagrammatic view of partial elements of the
light source while targets are generated by a fuel target
generator, in accordance with some embodiments.
[0009] FIG. 4 is a flowchart of a method for a generating light, in
accordance with some embodiments.
[0010] FIG. 5 is a diagram of a signal intensity detected by a
detector versus time, in accordance with some embodiments.
[0011] FIG. 6 is a diagrammatic view of a light source in the
lithography system, in accordance with some embodiments.
DETAILED DESCRIPTION
[0012] The following disclosure provides many different
embodiments, or examples, for implementing different features of
the subject matter provided. Specific examples of solutions and
arrangements are described below to simplify the present
disclosure. These are, of course, merely examples and are not
intended to be limiting. For example, the formation of a first
feature over or on a second feature in the description that follows
may include embodiments in which the first and second features are
formed in direct contact, and may also include embodiments in which
additional features may be formed between the first and second
features, such that the first and second features may not be in
direct contact. In addition, the present disclosure may repeat
reference numerals and/or letters in the various examples. This
repetition is for the purpose of simplicity and clarity and does
not in itself dictate a relationship between the various
embodiments and/or configurations discussed.
[0013] Furthermore, spatially relative terms, such as "beneath,"
"below," "lower," "above," "upper" and the like, may be used herein
for ease of description to describe one element or feature's
relationship to another element(s) or feature(s) as illustrated in
the figures. The spatially relative terms are intended to encompass
different orientations of the device in use or operation in
addition to the orientation depicted in the figures. The apparatus
may be otherwise oriented (rotated 90 degrees or at other
orientations) and the spatially relative descriptors used herein
may likewise be interpreted accordingly. It should be understood
that additional operations can be provided before, during, and
after the method, and some of the operations described can be
replaced or eliminated for other embodiments of the method.
[0014] The advanced lithography process, method, and materials
described in the current disclosure can be used in many
applications, including fin-type field effect transistors
(FinFETs). For example, the fins may be patterned to produce a
relatively close spacing between features, for which the above
disclosure is well suited. In addition, spacers used in forming
fins of FinFETs can be processed according to the above
disclosure.
[0015] FIG. 1 is a schematic and diagrammatic view of a lithography
system 10, in accordance with some embodiments. The lithography
system 10 may also be generically referred to as a scanner that is
operable to perform lithography exposing processes with respective
radiation source and exposure mode.
[0016] The lithography system 10 includes a light source 12, an
illuminator 14, a mask stage 16, a mask 18, a projection optics
module (or projection optics box (POB)) 20 and a substrate stage
24, in accordance with some embodiments. The elements of the
lithography system 10 can be added to or omitted, and the invention
should not be limited by the embodiment.
[0017] The light source 12 is configured to generate radians having
a wavelength ranging between about 1 nm and about 100 nm. In one
particular example, the light source 12 generates an EUV light with
a wavelength centered at about 13.5 nm. Accordingly, the light
source 12 is also referred to as an EUV light source. However, it
should be appreciated that the light source 12 should not be
limited to emitting EUV light. The light source 12 can be utilized
to perform any high-intensity photon emission from excited target
material.
[0018] In various embodiments, the illuminator 14 includes various
refractive optic components, such as a single lens or a lens system
having multiple lenses (zone plates) or alternatively reflective
optics (for EUV lithography system), such as a single mirror or a
mirror system having multiple mirrors in order to direct light from
the light source 12 onto a mask stage 16, particularly to a mask 18
secured on the mask stage 16. In the present embodiment where the
light source 12 generates light in the EUV wavelength range,
reflective optics is employed.
[0019] The mask stage 16 is configured to secure the mask 18. In
some embodiments, the mask stage 16 includes an electrostatic chuck
(e-chuck) to secure the mask 18. This is because the gas molecules
absorb EUV light and the lithography system for the EUV lithography
patterning is maintained in a vacuum environment to avoid EUV
intensity loss. In the present disclosure, the terms mask,
photomask, and reticle are used interchangeably.
[0020] In the present embodiment, the mask 18 is a reflective mask.
One exemplary structure of the mask 18 includes a substrate with a
suitable material, such as a low thermal expansion material (LTEM)
or fused quartz. In various examples, the LTEM includes TiO2 doped
SiO2, or other suitable materials with low thermal expansion. The
mask 18 includes reflective multilayer deposited on the
substrate.
[0021] The reflective multilayer includes a plurality of film
pairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer
of molybdenum above or below a layer of silicon in each film pair).
Alternatively, the reflective multilayer may include
molybdenum-beryllium (Mo/Be) film pairs, or other suitable
materials that are configurable to highly reflect the EUV light.
The mask 18 may further include a capping layer, such as ruthenium
(Ru), disposed on the reflective multilayer for protection. The
mask 18 further includes an absorption layer, such as a tantalum
boron nitride (TaBN) layer, deposited over the reflective
multilayer. The absorption layer is patterned to define a layer of
an integrated circuit (IC). Alternatively, another reflective layer
may be deposited over the reflective multilayer and is patterned to
define a layer of an integrated circuit, thereby forming an EUV
phase shift mask.
[0022] The projection optics module (or projection optics box
(POB)) 20 is configured for imaging the pattern of the mask 18 on
to a semiconductor wafer 22 secured on a substrate stage 24 of the
lithography system 10. In some embodiments, the POB 20 has
refractive optics (such as for a UV lithography system) or
alternatively reflective optics (such as for an EUV lithography
system) in various embodiments. The light directed from the mask
18, carrying the image of the pattern defined on the mask, is
collected by the POB 20. The illuminator 14 and the POB 20 are
collectively referred to as an optical module of the lithography
system 10.
[0023] In the present embodiment, the semiconductor wafer 22 may be
made of silicon or other semiconductor materials. Alternatively or
additionally, the semiconductor wafer 22 may include other
elementary semiconductor materials such as germanium (Ge). In some
embodiments, the semiconductor wafer 22 is made of a compound
semiconductor such as silicon carbide (SiC), gallium arsenic
(GaAs), indium arsenide (InAs), or indium phosphide (InP). In some
embodiments, the semiconductor wafer 22 is made of an alloy
semiconductor such as silicon germanium (SiGe), silicon germanium
carbide (SiGeC), gallium arsenic phosphide (GaAsP), or gallium
indium phosphide (GaInP). In some other embodiments, the
semiconductor wafer 22 may be a silicon-on-insulator (SOI) or a
germanium-on-insulator (GOI) substrate.
[0024] In addition, the semiconductor wafer 22 may have various
device elements. Examples of device elements that are formed in the
semiconductor wafer 22 include transistors (e.g., metal oxide
semiconductor field effect transistors (MOSFET), complementary
metal oxide semiconductor (CMOS) transistors, bipolar junction
transistors (BJT), high voltage transistors, high-frequency
transistors, p-channel and/or n-channel field-effect transistors
(PFETs/NFETs), etc.), diodes, and/or other applicable elements.
Various processes are performed to form the device elements, such
as deposition, etching, implantation, photolithography, annealing,
and/or other suitable processes. In some embodiments, the
semiconductor wafer 22 is coated with a resist layer sensitive to
the EUV light in the present embodiment. Various components
including those described above are integrated together and are
operable to perform lithography exposing processes.
[0025] The lithography system 10 may further include other modules
or be integrated with (or be coupled with) other modules. In the
present embodiment, the lithography system 10 includes a gas supply
module 26 designed to provide hydrogen gas to the light source 12.
The hydrogen gas helps reduce contamination in the light source
12.
[0026] FIG. 2 illustrates the light source 12 in a diagrammatical
view, in accordance with some embodiments. The light source 12
employs a dual-pulse laser produced plasma (LPP) mechanism to
generate plasma and further generate EUV light from the plasma.
[0027] In some embodiments, the light source 12 includes a
controller 13, a fuel target generator 30, a laser generator LG, a
laser produced plasma (LPP) collector 60 and a monitoring device
70. The above-mentioned elements of the light source 12 may be held
under vacuum. It should be appreciated that the elements of the
light source 12 can be added to or omitted, and the invention
should not be limited by the embodiment.
[0028] The fuel target generator 30 is configured to generate a
plurality of targets 82. In some embodiments, the fuel target
generator 30 includes a vessel 31 for containing a target material
(not shown in figures) and a gas supplier 32. The gas supplier 32
is connected to the vessel 31 and configured to supply a pumping
gas 33 into the vessel 31. The pumping gas 33 increases the
pressure in vessel 31 so as to force target material contained in
the vessel 31 out of the fuel target generator 30 and drive the
flowing of the targets 82.
[0029] In some embodiments, a flow velocity of the targets 82 from
the fuel target generator 30 is a function of the pressure of the
pumping gas 33 in the fuel target generator 30. For example, the
targets 82 flow faster when the pressure of the pumping gas 33 in
the vessel 31 is increased, and the targets 82 flow slower when the
pressure of the pumping gas 33 in the vessel 31 is reduced.
[0030] In some embodiments, the fuel target generator 30 further
includes a nozzle 34 and an actuator 35. The nozzle 34 is connected
to the vessel 31 for dispensing the targets 82, and the actuator 35
surrounds the nozzle 34. The actuator 35, for example, includes a
piezoelectic material. The actuator 35 applies a force on the
nozzle 34 in response to control signal from the controller 13 so
as to supply the targets 82 with a predetermined mode.
[0031] For example, the controller 13 supplies a voltage to the
actuator 35 at a given frequency, causing the actuator 35 to press
the nozzle 34 at the time of receiving the voltage and stop the
pressing when no voltage is received. As a result, the nozzle 34
may supply a plurality of targets 82 in the form of micro-droplets
into the excitation zone 81. In some other embodiments, a droplet
pitch between two neighboring targets 82 and/or the diameter of the
targets 82 are controlled as a function of the frequency at which
the voltage is supplied to the actuator 35.
[0032] In an embodiment, the targets 82 are tin (Sn) droplets. In
an embodiment, the targets 82 each have a diameter about 30 microns
(.mu.m). In an embodiment, the targets 82 are generated at a rate
about 50 kilohertz (kHz) and are introduced into a zone of
excitation 81 in the light source 12 at a speed about 70 meters per
second (m/s). Other material can also be used for the targets 82,
for example, a tin containing liquid material such as eutectic
alloy containing tin, lithium (Li), and xenon (Xe). The targets 82
may be in a solid or liquid phase.
[0033] The laser generator LG is configured to generate at least
one laser to allow a conversion of the targets 82 into plasma. In
some embodiments, the laser generator LG includes a first laser
source 40 and a second laser source 50. The first laser source 40
is configured to produce a pre-pulse laser 42. The second laser
source 50 is configured to produce a main pulse laser 52. The
pre-pulse laser 42 is used to heat (or pre-heat) the targets 82 to
expand the targets 82, which is subsequently irradiated by the main
pulse laser 52, generating increased emission of light.
[0034] In an embodiment, the first laser source 40 is a carbon
dioxide (CO2) laser source. In another embodiment, the first laser
source 40 is a neodymium-doped yttrium aluminum garnet (Nd:YAG)
laser source. In an embodiment, the second laser source 50 is a CO2
laser source.
[0035] In the present embodiment, the pre-pulse laser 42 has less
intensity and a smaller spot size than the main pulse laser 52. In
various embodiments, the pre-pulse laser 42 has a spot size of
about 100 .mu.m or less, and the main pulse laser 52 has a spot
size about 200-300 .mu.m, such as 225 .mu.m. The pre-pulse laser 42
and the main pulse laser 52 are generated to have certain driving
powers to fulfill wafer volume production, such as a throughput of
125 wafers per hour. For example, the pre-pulse laser 42 is
equipped with about 2 kilowatts (kW) driving power, and the main
pulse laser 52 is equipped with about 19 kW driving power. In
various embodiments, the total driving power of the pre-pulse laser
42 and the main pulse laser 52, is at least 20 kW, such as 27 kW.
However, it should be appreciated that many variations and
modifications can be made to embodiments of the disclosure.
[0036] The pre-pulse laser 42 and main pulse laser 52 are directed
through windows (or lenses) 44 and 54, respectively, into the zone
of excitation 81 and irradiate targets 82 at a first lighting
position LP1 and a second lighting position LP2. The windows 44 and
54 adopt a suitable material substantially transparent to the
respective laser beams. The method for exciting the targets 82
supplied by the fuel target generator 30 is described later.
[0037] The monitoring device 70 is configured to monitor conditions
of the targets 82 supplied by the fuel target generator 30. In some
embodiments, the monitoring device 70 includes a transducer 71 and
a detector 72. The transducer 71 is configured to generate one or
more detection signals for monitoring conditions of the targets 82,
and the detector 72 is configured to receive the detection signal
reflected by the targets 82.
[0038] In some embodiments, as shown in FIG. 3, the transducer 71
includes two light emitters, such as first light emitter 711 and
second light emitter 712. The first light emitter 711 continuously
generates a first light curtain L1 during the supply of the targets
82. The second light emitter 712 continuously generates a second
light curtain L2 during the supply of the targets 82. The first
light emitter 711 and the second light emitter 712 are arranged so
that a first detection position DP1 and a second detection position
DP2 are illuminated by the first light curtain L1 and the second
light curtain L2. The light curtain L 1 and the light curtain L2
may each include a number of light beams arranged sequentially
along a straight line or curved line. In some other embodiments,
each of the first light emitter 711 and the second light emitter
712 generates a single light beam to a respective one of the first
detection position DP1 and the second detection position DP2.
[0039] In some embodiments, the first detection position DP1 and
the second detection position DP2 are arranged on a moving path 85
along which the targets 82 are moved. The first detection position
DP1 and the second detection position DP2 are spaced apart by a
distance D. The distance D is smaller than a droplet pitch P
between two neighboring targets 82. The ratio between the distance
D and the droplet pitch P may be about 0.1 to about 0.9. The ratio
between the distance D and the droplet pitch P may be about 0.3 to
about 0.5. The light curtain L1 and the light curtain L2 may each
include a number of light beams arranged sequentially along a
straight line or curved line. In some other embodiments, each of
the first light emitter 711 and the second light emitter 712
continuously emits one single light beam.
[0040] The first light emitter 711 and the second light emitter 712
may emit radiation such as laser having wavelength about 1070 nm.
The driving power of the radiation emitted by the first light
emitter 711 and the second light emitter 712 is sufficiently less
than the driving power of the pre-pulse laser 42 and the main pulse
laser 52. The radiation from the first light emitter 711 and the
radiation from the second light emitter 712 may be different or the
same. For example, the wavelength of radiation emitted from the
first light emitter 711 is higher than the wavelength of the
radiation from the second light emitter 712 for increasing
detection accuracy.
[0041] The detector 72 is arranged adjacent to the transducer 71 so
as to receive light reflected from the first detection position DP1
and the second detection position DP2 when an individual target 82
passes through the first detection position DP1 and the second
detection position DP2. In some embodiments, the front surface 721
of the detector 72 that is used for receiving the signals is not
parallel to the moving path 85 and is oriented toward the fuel
target generator 30. The front surface 721 may be inclined relative
to the moving path 85 so that the reflected first light curtain L1
and the reflected second light curtain L2 are perpendicularly
projected on the front surface 721. As a result, the detected
intensity of the first light curtain L1 and the second light
curtain L2 is maximized and noise caused by the pre-pulse laser 42
and the main pulse laser 52 is minimized.
[0042] By recording the time when the light reflected from the
first detection position DP1 is detected and by recording the time
when the light reflected from the second detection position DP2 is
detected, the period of time during which an individual target 82
passes through the first detection position DP1 and the second
detection position DP2 can be measured. In some embodiments, the
detector 72 is electrically connected to the controller 13. The
measured result is transmitted to the controller 13 by the detector
72 for further processing.
[0043] It should be appreciated that while there is only one
detector 72 arranged for detecting the reflected light, many
variations and modifications can be made to embodiments of the
disclosure. In some other embodiments, there are two detectors 72
are used to receive light reflected from the first detection
position DP1 and the second detection position DP2.
[0044] In addition, while the embodiment shown in FIG. 3 uses
optical signals (e.g., laser) for measuring the period of time that
targets pass two detection positions, other technique can be
utilized for measuring the period of time. For example, the
monitoring device 70 may include a camera and an image analyzer.
The camera is used to capture images of the targets 82 when they
pass through the first detection position DP1 and the second
detection position DP2. With the recorded images, the period of
time that the individual target passes two detection positions can
be measured by analyzing the images of the first detection position
DP1 and the second detection position DP2 with an image
analyzer.
[0045] The controller 13 is configured to control one or more
elements of the light source 12. In some embodiments, the
controller 13 is configured to drive the fuel target generator 30
to generate the targets 82. In addition, the controller 13 is
configured to drive the first laser source 40 and the second laser
source 50 to fire the pre-pulse laser 42 and the main pulse laser
52. The generation of the pre-pulse laser 42 and the main pulse
laser 52 may be controlled to be associated with the generation of
targets 82 by the controller 13 so as to make the pre-pulse laser
42 and the main pulse laser 52 hit each target 82 in sequence.
Moreover, the controller 13 is configured to control the supply of
pumping gas 91 from the gas supplier 32 into the fuel target
generator 30 so as to change the flow velocity of the targets 82
from the fuel target generator 30.
[0046] The controller 13 may be a computer system. In one example,
the computer system includes a network communications device or a
network computing device (for example, a mobile cellular phone, a
laptop, a personal computer, a network server, etc.) capable of
communicating with a network. In accordance with embodiments of the
present disclosure, the computer system performs specific
operations via a processor executing one or more sequences of one
or more instructions contained in a system memory component.
[0047] The processor may include a digital signal processor (DSP),
a microcontroller (MCU), and a central processing unit (CPU). The
system memory component may include a random access memory (RAM) or
another dynamic storage device or read only memory (ROM) or other
static storage devices, for storing data and/or instructions to be
executed by the processor. For example, the system memory component
may store a predetermined value of a flow velocity of targets, a
predetermined value of the period of time during an individual
target passe two detection position, or an acceptable range for
adjusting parameter of the laser generator.
[0048] FIG. 4 is a flowchart of a method 90 for generating a light,
in accordance with some embodiments. For illustration, the flow
chart will be described along with the drawings shown in FIGS. 1-3
and 5. Some of the described transportation stages can be replaced
or eliminated in different embodiments.
[0049] The method 90 includes operation 91, in which targets 82 are
generated by forcing the target material out of the droplet
generator 30. In some embodiments, the fuel target generator 30
shown in FIG. 2 is configured to generate the targets 82. The fuel
target generator 30 is controlled to generate targets 82 with the
proper material, proper size, proper frequency, and proper flow
velocity and direction according to a processing recipe.
[0050] The method 90 also includes operation 92 in which the period
of time during which one of the targets 82 passes through the first
detection position DP1 and the second detection position DP2 is
measured. In some embodiments, operation 92 is performed by the
monitoring device 70. As shown in FIG. 3, the first light curtain L
1 and the second light curtain L2 from the transducer 71
continuously illuminate on the first detection position DP1 and the
second detection position DP2, respectively.
[0051] When one of the targets 82 passes through the first
detection position DP1 at time t1, the first light curtain L1 is
reflected by the target 82 and detected by the detector 72. In
addition, when the targets 82, as indicated by dotted line, passes
through the second detection position DP2 at time t2, the second
light curtain L2 is reflected by the target 82 and detected by the
detector 72.
[0052] One embodiment of the detection result of the detector 72 is
shown diagram of FIG. 5. A period of time At between time t1 and
time t2 can be measured by subtracting the time t2 by the time t1.
In some embodiments, radiation from the pre-pulse laser 42 or the
main pulse laser 52 is also detected by the detector 72 and
produces signal at time t3. This noise signal may be mitigated by
positioning the detector 72 in a proper manner, or by utilizing a
filtering technique to ignore signal having intensity less than
I.sub.min.
[0053] The method 90 also includes operation 93, a flow velocity of
the targets 82 is calculated. In some embodiments, the data
associated the time difference At is sent to the controller 13. The
controller 13 calculates flow velocity of the targets 82 by
dividing the distance D (FIG. 3) by the measured time difference
.DELTA.t. Afterwards, the method 90 continues with operation 94, in
which the controller 13 determines if the calculated flow velocity
is different from a predetermined value of the predetermined
processing recipe.
[0054] When the calculated flow velocity is the same as the
predetermined value of the predetermined processing recipe, the
method continues with operation 95. In operation 95, the targets 82
are excited to generate light. One method for exciting the targets
82, in accordance with some embodiments, is described below.
[0055] In the beginning, the first laser source 40 is used to
generate the pre-pulse laser 42 to expand the targets 82 at the
first lighting position LP1. Before being irradiated by the
pre-pulse laser 42, the targets 82 have circular shape. After the
targets 82 are irradiated by the pre-pulse laser 42, a portion of
the pre-pulse laser 42 is converted to kinetic energy to transform
the targets 82 to expanded targets 83 with pancake-shape, as shown
in FIG. 2.
[0056] Afterwards, the second laser source 50 is used to generate
the main pulse laser 52 to excite the expanded targets 83 at the
second lighting position LP2. The main pulse laser 52 heats the
expanded targets 83 to a preset temperature. At the preset
temperature, the target material 80 in the expanded targets 83 shed
their electrons and become a plasma that emits light 84.
[0057] In some embodiments, the first laser source 40 is configured
to generate the pre-pulse laser 42 after a time interval when the
detector 72 receives the first light curtain L1. Because the
targets 82 are moved as the desired flow velocity and because an
intermediate distance between the first detection position DP1 and
the first lighting position LP1 is fixed, the time interval can be
calculated by dividing the intermediate distance by the desired
flow velocity. As a result, the targets 82 can be accurately
irradiated by the pre-pulse laser 42 when the targets 82 reach the
first lighting position LP1.
[0058] On the other hand, when the calculated flow velocity is
different from the preset value of the predetermined processing
recipe, the method continues with operation 96. In operation 96,
the parameter of the laser generator LG is adjusted. In some
embodiments, the firing time or the firing frequency of the
pre-pulse laser 42 and the main pulse laser 52 is adjusted by the
controller 13 according to the calculated flow velocity so as to
accurately irradiate the targets 82 once the targets 82 get the
first lighting position LP1 and the second lighting position
LP2.
[0059] For example, when the calculated flow velocity is greater
than the predetermined value of the predetermined processing
recipe, which means many more targets will pass through the first
lighting position LP1 and the second lighting position LP2, an
increase in the firing frequency may allow most of the targets 82
to be irradiated by the pre-pulse laser 42 and the main pulse laser
52. Conversely, when the calculated flow velocity is less than the
predetermined value of the predetermined processing recipe, a
decrease in the firing frequency may allow most of the targets 82
to be irradiated by the pre-pulse laser 42 and the main pulse laser
52.
[0060] In some embodiments, in the cases where the distance D
between the first detection position DP1 and second detection
position DP2 is fixed, operation 93 is omitted, and the measure
period of time is compared with a predetermined value associated a
desired period of time according to a processing recipe. It should
be noted that the predetermined value described above may be refer
to as a specific value, a range of value, or multiple ranges of
value.
[0061] The method 90 also includes operation 97, in which the
operating status of the laser generator LG is monitored to
determine if the adjustment of the laser generator LG is outside of
an acceptable range. In some embodiments, an upper limit firing
frequency and a lower limit firing frequency are set by the
controller 13. When the desired firing frequency associated the
calculated flow velocity is within an acceptable range between the
upper limit firing frequency and the lower limit firing frequency,
the controller 13 actuates the adjustment of the laser generator
LG, and the method continues to operation 95.
[0062] On the other hand, when the desired firing frequency
associated the calculated flow velocity is outside of the
acceptable range between the upper limit firing frequency and the
lower limit firing frequency, the controller 13 may not adjust the
laser generator LG to the desired firing frequency, and instead at
least one parameter of the fuel target generator 30 is adjusted
(operation 98). This is because irradiating the targets 82 with
lasers having a firing frequency that is higher than the upper
limit may cause the light source to become contaminated by debris,
and because irradiating the targets 82 using lasers with a firing
frequency that is less than the lower limit may lead to a decrease
in the power of the light 84.
[0063] In some embodiments, in operation 98, the pressure of the
pumping gas 33 in the fuel target generator 30 is modified so that
the flow velocity of the targets 82 from the fuel target generator
30 is adjusted accordingly. A method for determining the modified
pressure of the pumping gas 33 may include calculating difference
between the detected flow velocity or the measured period of time
and the predetermined value. The method further includes comparing
the calculated difference with a lookup table (not shown) to
determine the amount of pressure required to increase or
decrease.
[0064] In some other embodiments, the frequency of the voltage
supplied to the actuator 35 is changed, so that the frequency for
generating the targets 82 is adjusted accordingly. With such
adjustments to the parameters of the fuel target generator 30, the
targets 82 can be irradiated with the pre-pulse laser 42 and the
main pulse laser 52 at the proper angle and energy, and the power
conversion efficiency of the targets to the light is improved.
[0065] It should be appreciated that while operation 98 is
performed after operations 96 and 97, the embodiments should not be
limited thereto. In some other embodiments, operations 96 and 97
are omitted, and operation 98 is initiated right after operation 94
when the flow velocity is different from the predetermined value.
Alternatively, operation 96 and operation 98 can be performed the
same time. That is, the conditions of the targets 82 are modified
to a desired mode by simultaneously adjusting parameters of the
laser generator LG and the fuel target generator 30.
[0066] In some other embodiments, if the adjusted parameter of the
fuel target generator 30 is outside of an acceptable range, a
warning signal is issued by the controller 13. The warning signal
is sent to the fuel target generator 30 to stop the supply of the
targets 82. In addition, the warning signal triggers the operation
of warning equipment (such as a warning light or warning ring not
shown in figures) to call a personnel to perform a maintenance
process.
[0067] The method 90 may be performed before a beginning of a
lithography exposure process. Alternatively, the method 90 may be
periodically performed after a given amount of semiconductor wafers
are process the by the lithography system 10. Alternatively, the
method 90 may be performed during the lithography exposure
process.
[0068] FIG. 6 is a diagrammatic view of the light source 12a in the
lithography system, in accordance with some embodiments. In the
embodiments shown in FIG. 6, elements that are similar to those
shown in FIG. 2 are provided with the same reference numbers, and
the features thereof are not reiterated in the interests of
brevity. Differences between the light source 12a and the light
source 12 include the light source 12a including two monitoring
devices 70. In some embodiments, the additional monitoring device
70 is arranged such that the condition of expanded targets 83 can
be detected.
[0069] In some embodiments, the additional monitoring device 70 can
detect more than the flow velocity of the expanded targets 83. For
example, by calculating the duration of the reflected light curtain
received by the additional monitoring device 70, the length of the
expanded targets 83 can be detected. With such additional
information about the expanded targets 83, the expanded targets 83
can be accurately irradiated with the main pulse laser 52, and
higher power conversion can be achieved.
[0070] Embodiments of a method for generating light in lithography
exposure process are provided. Parameters of a light source are
adjusted according to collected information of the targets during
the lithography exposure process. Therefore, light emission
conversion efficiency is enhanced, and contamination of the light
emitting system by debris is reduced.
[0071] In accordance with some embodiments, a method for generating
light in lithography exposure process is provided. The method
includes generating targets with a fuel target generator. The
method further includes measuring a period of time during which one
of the targets passes through two detection positions on a moving
path along which the targets move. The method also includes
exciting the targets with a laser generator so as to generate
plasma that emits light. In addition, the method includes adjusting
at least one parameter of the fuel target generator or the laser
generator according to the measured period of time, when the
measured period of time is different from a predetermined
value.
[0072] In accordance with some embodiments, a method for generating
light in lithography exposure process is provided. The method
includes generating targets with a fuel target generator. The
method further includes detecting a flow velocity of the targets.
The method also includes adjusting the flow velocity of the targets
in response to the detected flow velocity when the detected flow
velocity is different from a predetermined value. In addition, the
method includes irradiating at least one laser on the targets to
generate plasma that emits light.
[0073] In accordance with some embodiments, a light source for
generating light in lithography system is provided. The light
source includes a fuel target generator configured to generate a
plurality of targets along a moving path. The light source further
includes a monitoring device configured to measure a period of time
during which one of the targets passes through two detection
positions. The light source also includes a laser generator
configured to generate at least one laser to allow a conversion of
the targets into plasma. In addition, the light source includes a
controller configured to adjust a parameter of the fuel target
generator according to the measured period of time, when the
measured period of time is different from a predetermined
value.
[0074] Although the embodiments and their advantages have been
described in detail, it should be understood that various changes,
substitutions, and alterations can be made herein without departing
from the spirit and scope of the embodiments as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods, and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure, processes, machines, manufacture, compositions of
matter, means, methods, or steps, presently existing or later to be
developed, that perform substantially the same function or achieve
substantially the same result as the corresponding embodiments
described herein may be utilized according to the disclosure.
Accordingly, the appended claims are intended to include within
their scope such processes, machines, manufacture, compositions of
matter, means, methods, or steps. In addition, each claim
constitutes a separate embodiment, and the combination of various
claims and embodiments are within the scope of the disclosure.
* * * * *